1. Field of the Invention
The invention relates in general to an improved electronic pen measurement system.
2. Description of the Related Art
Concerning circuits that sense analog signals, Sigma-Delta Analog to Digital Converters (ΣΔADC) have been known some time for performing simple analog to digital conversion, but have recently become very popular as programmable logic clock speeds have improved to the point where very good conversion function is possible. Many new ideas and work centered on improving these converters speed and functionality has been in an effort to allow this more digital conversion method to replace the more standard analog techniques. In the touch realm many improvement patents have been granted around incorporation of known capacitive sampling techniques and Delta Sigma conversion of analog to digital.
U.S. Pat. No. 8,089,289 has an example of prior art technology using a Delta Sigma Converter and showing mutual capacitive scheme using square wave drive and switched capacitor function with rectification in two embodiment drawings of the same function, as shown in FIG. 20.
U.S. Pat. No. 7,528,755 shows an example of prior art technology using a Delta Sigma Converter and showing scheme capable of signal drive or measure technique selectable via a mux as shown in FIG. 21.
U.S. Pat. No. 8,547,114 shows an example of prior art technology using a Delta Sigma Converter and switched capacitor techniques as shown in FIG. 22.
U.S. Pat. No. 8,587,535 shows an example of a prior art strategy, this state of the art mutual capacitance multi-touch system with simultaneous digital square wave patterned transmission and simultaneous receive with synchronous demodulation and pen capable, as shown in FIG. 23. This system does not allow multi-mode concurrent touchscreen sampling, does not have true simultaneous sampling due to each row using a different bit pattern which effectively scrambles the noise distribution on receipt, is not capable of self-capacitance measurements, and due to the use of square wave drive has a receive signal spectrum that contains the primary frequency as well as its harmonics which necessitate lower trace impedance to prevent attenuation of the higher harmonics across the panel.
Therefore, a need exists for a much faster sampling method that can acquire data simultaneously for different modes of, for example, self, mutual, and pen, and with simultaneous sampling of the different channels.
Also, in some applications, to reduce the sample time via signal to noise ratio improvement where possible, continuous sampling schemes and advanced filter methods, modulation and demodulation schemes, and digital domain methods are needed. To keep the cost and power usage as low as possible the circuitry should be as much in the digital realm as possible.
Finally, many different touch sensors are now available that work through the measurement of changes to impedance, and providing a system that can handle multiple sensor types and configurations, including those currently known and those to be developed in the future, is also greatly desired.
Concerning electronic pens, pressure, tilt, and barrel rotation are a part of writing and inking characteristics and even children are aware of the differences to a resultant pencil or crayon line characteristics caused by these three different manipulations of a writing instrument.
Digitizing pens in the electromagnetic and electrostatic realm typically include a method of measuring and transmitting the tip pressure to the receiving system. The receiving system may include durable glass providing high optical transparency for viewing images displayed by an underlying display device that displays images such as graphical buttons and icons or an opaque system. When a user writes, for example with a pen, on the outer surface of the substrate on the display device, the pen sends a signal that the receiving system interprets and resolves to a location determined by sensing amplitude differences between the receiving system electrodes, and through modulation or pulse timing the pressure value is transmitted using the same signal frequency as the location signal.
U.S. Pat. No. 5,633,471A shows an example of prior art technology using a pressure sensor disk to measure the pressure transmitted through the pen tip as shown in FIG. 41.
Pressure has typically been measured internal to the pen body with a single motion axis sensor measuring changes to resistance, capacitance, inductance, or light intensity. These solutions typically work through a motion of a rod mechanism transmitting axial force from the tip of the pen to the sensor mechanism. As seen from the above drawing the result versus pressure curve is non-linear. The disadvantage to the aforementioned solutions is the drop in transmitted force to the sensor as the pen is tilted towards the surface.
Tilt determination is very important to prior and state of the art electromagnetic and electrostatic pen systems. In a typical system the pressure signal decreases as the tilt increases by the cosine of the tilt angle. Without a method of measuring the tilt angle the pressure determination becomes more and more unsure.
U.S. Pat. No. 5,414,227 shows an example of tilt and orientation using a plural set of continuous ring electrodes for transmit and receive as shown in FIG. 42.
In some pen systems the tilt and orientation of the pen are determined through two electrodes, the primary location electrode and a secondary vertically displaced electrode. At some angle of tilt the two received signals show orientation and tilt.
In some pen systems the tilt and rotation position of the pen barrel are determined through extra signal producing transmitters around the tip main transmitter. These transmitters inject a signal relative to the electrode position and the proximity of the sensor and the relative energy distribution of the said energy to the rows and columns.
U.S. Pat. No. 8,963,889B2 shows an example of tilt and rotation using the tip and an extra single or broken ring electrode elements as shown in FIG. 43.
U.S. Pat. No. 8,638,320 B2 shows an example of tilt and rotation using the shape of the tip or tip and extra broken ring electrode elements as shown in FIG. 44.
Distance from the detecting surface greatly reduces the capacitance coupling energy of a shaped electrode or separate electrodes. If alternate frequencies or digital bit patterns are used these methods can be effective but have some limitations. For example, a shaped electrode does not show rotation orientation and even at angles less than 45 deg from the perpendicular the detection shape will not have enough information for an accurate tilt.
Using multiple electrodes solves the perpendicular rotation orientation and tilt angle resolution at low perpendicular angles through increased pen and system complexity but at higher angles only a single separate electrode will present to the surface of the sensor and so at higher angles barrel rotation resolution will be low but tilt angle is improved. Pressure and tilt have good resolution at 45 deg but at the pen barrel becomes flatter to the surface plane the pressure resolution drops.
FIG. 37 A diagram showing the multi electrode solution broken ring solution resolutions at different pen angles and also showing the multi electrode continuous ring solution resolutions at different pen angles.
Even in state of the art solutions FIG. 44 using a broken ring electrode solution the pressure and barrel rotation resolutions drop at low angles to the plain.
Pressure and tilt on these prior art systems is heavily linked but the values are produced through very different and separate mechanisms with different resolutions, noise characteristics, and group delays.
“Hover” is the ability of digitizing pens to interact with the system without touching the surface. Surface contact typically indicating an inking or clicking action. Electromagnetic (EMR) and electrostatic (ES) systems by default work without direct contact to the electrodes. EMR and ES pen systems generally have hover capability for which distance from the surface is limited mostly due to signal to noise considerations. While ES systems hover's location is good, orientation, tilt, and barrel rotation has not generally been usable due to poor signal resolutions.
“Motion Detection” is the ability for a device to, at a minimum, determine if it has been moved. A simple motion detection can be useful on a digitizer pen as a low power to high power mode. Advanced schemes exist to measure this such as micro machined cantilever beam accelerometers or such. These systems have been reduced to small size, work well, and have much reduced cost but are still system cost adders.
“Proximity Detection” is the ability for the device to determine if it has been picked up, set down, or if it is close to the touch surface. This would typically be a self-capacitance measurement on grounded systems but generally would be measured through multiple electrodes and a mutual capacitance measurement.
“Ground System” in pen systems the ground path is often neglected and assumed low impedance which is definitely not the case. Any current transmitted through the pen tip primary electrode or secondary electrodes to a receiving system must also pass through the barrel of the pen, the users body, the air space surrounding the user or through the floor and finally to the system which may also be floating and so only the small capacitance between the user and the device containing the receiving system may be present. These paths represent variable impedances
Therefore, a need exists for a method of improved pressure, tilt, barrel rotation for normal and extended pen angles generated from a single system of internal measurements as well as other capabilities such as proximity, switch detection, slider, and high resolution touch zone sensing.